A special device known as an ophthalmoscope can be used to look at the fundus (back) of the eye through the pupil and examine structures like the retina, optic nerve, blood vessels and the choroid coat. This examination is known as ophthalmoscopy or funduscopy ("fundus" is the Latin word for "bottom" or "base"). About 20 minutes before the examination, the pupils of the eyes are dilated (enlarged) using eye drops.
In the direct exam, the doctor positions the ophthalmoscope close to the eye and shines a beam of light directly into it to see a small magnified section of the back of the eye. This is particularly useful for examining the structures at the center of the eye's fundus, including the optic nerve, the blood vessels and the macula.
In the indirect exam, the doctor uses a condensing lens with a bright light to examine the eye from a distance of about 60 centimeters. This allows them to see a larger area of the fundus, providing a better overview as well as a three-dimensional image. A slit lamp is sometimes used at the same time. Doing so greatly magnifies the retina and provides better lighting.
Conditions such as retinal detachment and optic nerve damage can be diagnosed using ophthalmoscopy. It can also be a good idea to examine the small blood vessels in the eye in people who have diabetes or high blood pressure because both of these conditions can damage blood vessels in the eye.
If your pupils are dilated using eye drops, your eyes will be very sensitive to light and your vision will be blurred for a few hours after the examination. For this reason, you are only allowed to drive a car or operate machinery again once the effect of the eye drops has worn off.